This invention relates to water-pressure booster systems in general, and to an improved low-flow shut-down control arrangement for water-pressure booster systems, in particular.
Water pressure booster systems receive water from a main conduit under a normally relatively low inlet pressure and raise the water pressure to a desired level by operating one or more pumps in relation to relative demand. Typically, a pressure-regulating or pressure reducing valve is interposed between the output of each pump and the system outlet conduit to regulate the system output pressure to a predetermined constant level.
In typical water pressure booster system operation, at least one of the pumps is kept running at all times to maintain building water pressure in distribution piping. Although this method does not require a pressurizing storage tank, energy is wasted by driving the pump during periods of minimal water usage.
It is desirable, therefore, to stop all pumps in the pressure booster system during very low water demand periods, such as during late evening or early morning hours, to conserve energy and to minimize the wear on the pumps and associated control equipment.
Previously various means and devices have been utilized to sense the proper moment to stop and start pump operation. Specifically some of these means and devices are pressure actuated switches, fixed temperature actuated switches, flow actuated switches and combinations thereof. U.S. Pat. No. 3,639,081 describes the prior uses of these various devices and additionally provides one solution to the problem of pump control under minimum flow conditions by monitoring both fluid flow and pressure.
In other prior systems which are commercially available, a fixed temperature actuated switch is utilized. More specifically the fixed temperatures actuated switch monitors the actual temperature of discharging water from the pump volute and stops the pump at a specific temperature. Accordingly, the fixed temperature switch must be set higher than the highest anticipated incoming water temperature to avoid untimely shut down. Since the incoming water temperatures varies throughout the year, the setting of the switch is difficult to determine. Furthermore, the specific temperature setting requires a greater temperature rise to shut-down the pump when the main conduit water is cool than when the water is warmer. Thus, under minimal flow conditions when the conduit water is cool, a fixed temperature switch controlled system may operate the pump for a considerably longer time period than when the conduit water is warm and accordingly energy is wasted.